Fluorescence visualization of Ia antigens on T cells

Abstract Visualization with the fluorescence microscope of Ia antigens on T cells has previously not been successful. In this paper we have used fluorescence hapten-sandwich labeling to examine cells for the simultaneous display of Ia antigens and T-cell-specific antigens. In contrast to small unstimulated T cells which bear only small amounts of Ia antigens, we find that concanavalin A-stimulated T-cell blasts exhibit amounts that are clearly recognizable. The predominant specificity expressed is encoded by the I -A subregion and appears to be indistinguishable from that on B cells. Smaller subpopulations exhibit products coded by the I -C and I -J subregions. Separation of subpopulations of T cells on the basis of selective display of Ia antigens appears only to be feasible with stimulated cells.